For the most part, in the past, the synthesis of hydrogen peroxide was accomplished by the hydrogenation of anthraquinone to form the corresponding hydroquinone and the subsequent oxidation of the hydroquinone to obtain hydrogen peroxide. The catalyst initially used to accomplish this reaction was Raney nickel which has only recently been replaced by a supported palladium catalyst. Although this process has been used since the 1940's through several modifications, it nevertheless is very capital intensive in terms of downstream separation process costs.
Among recent developments in the direct synthesis of hydrogen peroxide from hydrogen and oxygen, there may be mentioned Gosser et al. (U.S. Pat. No. 5,135,731) and Chuang et al. (U.S. Pat. No. 5,338,531) who have used palladium supported on silica and carbon, respectively, to carry out the reaction. In addition, U.S. Pat. No. 3,336,112 discloses a process for the direct production of hydrogen peroxide by contacting a mixture of gases containing oxygen hydrogen with a solid catalyst having a Group VIII metal included therein. U.S. Pat. No. 4,009,252 also discloses the same reaction utilizing a Group VIII metal catalyst.
One of the problems in using Group VIII metals, such as platinum and palladium, to catalyze the reaction of hydrogen and oxygen to form hydrogen peroxide is that these very same metals catalyze the reaction of hydrogen peroxide with hydrogen to produce water.
There have been many attempts to promote the reaction of hydrogen and oxygen to peroxide and to retard the reaction of hydrogen and hydrogen peroxide to produce water. One of the ways to increase the yield of hydrogen peroxide when using a Group VII metal catalyst is to conduct the reaction in the presence of halides. There is evidence that the presence of chloride and bromide ions have an important influence in promoting the Group VII metal-based catalytic scheme for producing hydrogen peroxide. The mechanism by which the halide ions promote the production of hydrogen peroxide is not clear but regardless of the mechanism, there are great concerns about using halides in such a reaction because of the extreme corrosive nature of halides when they are in solution.
U.S. Pat. No. 5,480,629 also uses Group VIII metals to catalyze the reaction of hydrogen and oxygen to peroxide by forming pillars of alkyl bisphosphonic acids with dicationic bipyridinium (viologen) groups incorporated into the alkyl chain. Within the pillars are Group VII metals which are dispersed throughout the organic compounds. This patent thus discloses a heterogeneous catalyst wherein an organic catalyst is a source of reducing potential to generate hydrogen peroxide from oxygen. The colloidal particles of Group VIII metals (e.g. platinum and/or palladium) act as catalysts for the preliminary step of removal of the electron from the hydrogen absorbed on the metal. The electrons released from this preliminary step reduce the viologen in the pore structure to give a radical cation. The radical cation will react with the dissolved oxygen and the hydrogen to form hydrogen peroxide.
In all of the processes described above, the decomposition reaction of hydrogen peroxide is enhanced the higher the peroxide levels.